In-plane switching mode liquid crystal display device and method for manufacturing the same

ABSTRACT

An in-plane switching mode LCD device and a method for manufacturing the same are disclosed, which are applicable to LCD device having a wide viewing angle, fineness and a wide size by using low resistance materials as source and drain electrode. A buffer layer is formed on an ohmic contact layer in the in-plane switching mode LCD.

[0001] This application claims the benefit of Korean Patent ApplicationNo. 2000-81949, filed on Dec. 26, 2000, the entirety of which is herebyincorporated by reference for all purposes as if fully set forth herein.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a display device, and moreparticularly, to an in-plane switching mode liquid crystal display (LCD)device and a method for manufacturing the same.

[0004] 2. Background of the Related Art

[0005] An in-plane switching mode LCD device is an LCD device having awide viewing angle, which has been developed for solving a problem ofhaving a narrow viewing angle in a Twisted Nematic LCD device. In thein-plane switching mode LCD device, common and pixel electrodes areformed on one substrate, and liquid crystals are driven by a horizontalelectric field generated between the common and pixel electrodes, sothat a viewing angle in the in-plane switching mode LCD device is widerthan a viewing angle in the Twisted Nematic LCD device.

[0006] A related art LCD device structure and a method for manufacturingthe same will be described with reference to the accompanying drawings.

[0007]FIG. 1A is a structural plan view illustrating a structure of therelated art in-plane switching mode LCD device. FIG. 1B is a plan viewtaken along line I-I′ of FIG. 1A.

[0008] As shown in FIG. 1A, the related art in-plane switching mode LCDdevice includes gate line 211 and data line 212 arranged on aninsulating substrate (not shown) to define a pixel region, a common line213 arranged within the pixel region in parallel with the gate line 211,a thin film transistor formed at a crossing point between the gate line211 and the data line 212, a pixel electrode 208 arranged within thepixel region in parallel with the data line 212 and connected with adrain electrode of the thin film transistor, and a common electrode 210arranged within the pixel region in parallel with the data line 212 andextending from the common line 213.

[0009] The thin film transistor will be described in detail withreference to FIG. 1B. A gate electrode 202 is formed on an insulatingsubstrate 201, and a gate insulating film 203 is formed on the surfaceof the insulating substrate 201 including the gate electrode 202. Then,a semiconductor layer 204 is formed like an island on the gateinsulating film 203 above the gate electrode 202, and an ohmic contactlayer 205 is formed on both sides of the gate electrode 202 on thesemiconductor layer 204. Source electrode 206 and drain electrode 207are formed at both sides of the gate electrode 202 above thesemiconductor layer 204. An ohmic contact layer 205 is formed betweenthe source and drain electrodes 206 and 207 and the semiconductor layer204. A pixel electrode 208 is formed on the drain electrode 207 and thegate insulating film 203. A passivation film 209 is deposited on thegate insulating film on which the pixel electrode 208 is formed, and acommon electrode 210 is formed on the passivation film 209.

[0010] Generally, in the related art LCD device shown in FIG. 1B, thegate insulating film 203 and the passivation film 209 may consist of asilicon nitride film (SiN_(x)). The gate electrode 202 may consist ofconductive materials such as copper (Cu), titanium (Ti), and chromium(Cr). The source electrode 206 and the drain electrode 207 may consistof chromium (Cr) in taking into consideration of the etching selectivitywith a transparent electrode.

[0011] A method for manufacturing the related art in-plane switchingmode LCD device will now be described with reference to FIG. 2A to FIG.2E.

[0012]FIG. 2A to FIG. 2E are plan views illustrating process steps formanufacturing the related art in-plane switching mode LCD device.

[0013] As shown in FIG. 2A, gate line materials and conductive metalmaterials, are deposited on the insulating substrate 201 by a processsuch as sputtering. Then, the gate electrode 202 is formed by apatterning process such as photolithography. The gate insulating film203 consisting of a silicon oxide film or a silicon nitride film, thesemiconductor layer 204 of amorphous silicon, and the ohmic contactlayer 205 of amorphous silicon containing n-type dopant, are depositedby a process such as plasma enhanced chemical vapor deposition (PECVD).

[0014] As shown in FIG. 2B, the semiconductor layer 204 and the ohmiccontact layer 205 formed on the gate insulating film 203, areselectively patterned.

[0015] As shown in FIG. 2C, a data line material, a conductive metalmaterial such as chromium (Cr), is deposited on the ohmic contact layer205 by a sputtering process, and the source electrode 206 and the drainelectrode 207 are formed by a patterning process such asphotolithography, so that the thin film transistor is formed.

[0016] As shown in FIG. 2D, the pixel electrode 208 is formed on thedrain electrode 207.

[0017] As shown in FIG. 2E, the passivation film 209 is deposited on thesubstrate, on which the above layers are deposited, by a plasma enhancedchemical vapor deposition (PECVD) process. The transparent commonelectrode 210 is formed on the passivation layer 209 using a conductivematerial such as indium tin oxide (ITO). Therefore, the manufacturingprocess steps of the related art LCD device are completed.

[0018] However, there are following problems in the related art in-planeswitching mode LCD device.

[0019] First, the pixel electrode occupies space within the pixel regionand so, an aperture ratio is reduced by an area occupied by the pixelelectrode.

[0020] The pixel electrode connected with the drain electrode can beformed as the transparent electrode for solving the problem of adecrease in the aperture ratio. However, if etching selectivity betweenthe transparent electrode and the drain electrode is not considered, thedrain electrode may be etched during patterning of the transparentelectrode. Therefore, reliability of the device may be degraded.

[0021] Furthermore, if the drain electrode material is selected takinginto consideration the etching selectivity ratio between the transparentelectrode and the drain electrode, chromium is the most appropriatematerial for the drain electrode.

[0022] But, since chromium has low electricity conductivity, andespecially affects resolution, there are limitations in implementing thein-plane switching mode LCD device having high resolution and a largesize.

SUMMARY OF THE INVENTION

[0023] Accordingly, the present invention is directed to an in-planeswitching mode LCD device and a method for manufacturing the same whichsubstantially obviates one or more problems due to limitations anddisadvantages of the related art.

[0024] An advantage of the present invention is to provide an in-planeswitching mode LCD device and a method for manufacturing the same thatare applicable to an LCD device having high resolution and a large sizeby improving brightness and aperture ratio without an additional mask.

[0025] Additional features and advantages of the invention will be setforth in the description which follows, and in part will be apparentfrom the description, or may be learned by practice of the invention.The objectives and other advantages of the invention will be realizedand attained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

[0026] To achieve these and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, thein-plane switching mode liquid crystal display device comprises a thinfilm transistor within a pixel region defined by a plurality of gatelines and data lines; and buffer layer is interposed between a gateelectrode and source and drain electrodes of the thin film transistor.The active region includes a gate electrode on an insulating substrate;a gate insulating film on an entire surface of the insulating substrateincluding the gate electrode; a semiconductor layer and an ohmic contactlayer on the gate insulating film; a buffer layer on the ohmic contactlayer to cover the semiconductor layer and the ohmic contact layer;source and drain electrodes on the buffer layer; a transparentconductive film for a pixel electrode connected with the drainelectrode; a passivation film on the pixel electrode; and a commonelectrode on the passivation film.

[0027] In another aspect of the present invention, a method formanufacturing the inplane switching mode LCD device includes selectivelydepositing a buffer layer on the insulating substrate deposited on thegate electrode, the gate insulating film, the semiconductor layer, andthe ohmic contact layer; patterning the buffer layer; forming thetransparent conductive film for the pixel electrode through the gateinsulating film and the buffer layer; and forming the source and drainelectrodes to connect with the transparent conductive film for the pixelelectrode.

[0028] In the in-plane switching mode LCD device according to thepresent invention, the buffer layer is formed on the ohmic contactlayer, so that the etching selectivity between the drain electrode andthe transparent conductive film is improved and it is possible toprevent the drain electrode from chemically reacting with the ohmiccontact layer.

[0029] It is to be understood that both the foregoing generaldescription and the following detailed description of the presentinvention are exemplary and explanatory and are intended to providefurther explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The accompanying drawings, which are included to provide afurther understanding of the invention and are incorporated in andconstitute a part of this application, illustrate embodiment(s) of theinvention and together with the description serve to explain theprinciple of the invention.

[0031] In the drawings:

[0032]FIG. 1A is a plan view illustrating a structure of a related artin-plane switching mode LCD device;

[0033]FIG. 1B is a plan view taken along line I-I′ of FIG. 1A;

[0034]FIG. 2A to FIG. 2E are sectional views illustrating manufacturingprocess steps in accordance with the related art in-plane switching modeLCD device;

[0035]FIG. 3 is a sectional view illustrating a structure of an in-planeswitching mode LCD device in accordance with the present invention; and

[0036]FIG. 4A to FIG. 4E are sectional views illustrating manufacturingprocess steps of the in-plane switching mode LCD device in accordancewith the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

[0037] Reference will now be made in detail to an embodiment of thepresent invention, examples of which are illustrated in the accompanyingdrawings.

[0038] Since a plan structure of an LCD device according to the presentinvention is the same as a structure of a related art LCD device, theplan structure of the LCD device according to the present invention willbe described with reference to the related art plan view.

[0039]FIG. 3 is a sectional view illustrating a structure of an in-planeswitching mode LCD device in accordance with the present invention,taken along line I-I′ of FIG. 1A. As shown in FIG. 3, the in-planeswitching mode LCD device according to the present invention includes aninsulating substrate 401; a gate electrode 402 formed on the insulatingsubstrate 401; a gate insulating film 403 formed on the insulatingsubstrate 401 including the gate electrode 402; a semiconductor layer404, an ohmic contact layer 405 and a buffer layer 406 deposited on thegate insulating film 403 at an upper portion of the gate electrode 402;a transparent pixel electrode 407 connected with the buffer layer 406;source electrode 408 and drain electrode 409 formed on the buffer layer406; a passivation layer 410 formed on an entire surface of theinsulating substrate 401 including the source electrode 408 and drainelectrode 409; and a common electrode 411 formed on the passivationlayer 410.

[0040] The gate electrode 402 is formed of a low resistance metal suchas aluminum (Al), copper (Cu), and silver (Ag).

[0041] The gate insulating film 403 is formed of a silicon nitride film(SiN_(x)), or a silicon oxide film (SiO_(x)) and the buffer layer 406 isgenerally formed of metal such as titanium (Ti).

[0042] As the buffer layer is formed, it is possible to prevent lowresistance metals used as the source and drain electrodes fromchemically reacting with the ohmic contact layer, and an etchingselectivity between the source and drain electrodes and the transparentpixel electrode is improved.

[0043] The manufacturing process steps of the in-plane switching modeLCD device will be described in more detail with reference to FIG. 4A toFIG. 4E.

[0044] As shown in FIG. 4A, one of the low resistance metals such asaluminum (Al), copper (Cu), and silver (Ag) is deposited on theinsulating substrate 401 by a sputtering process, and then the gateelectrode 402 is formed by a patterning process using photolithography.The gate insulating film 403 comprising a silicon nitride film or asilicon oxide film is formed on the insulating substrate 401 includingthe gate electrode 402. The semiconductor layer 404, the ohmic contactlayer 405, and the buffer layer 406 of titanium are formed on the gateinsulating film 403 by a PECVD process. At this time, the presence ofthe buffer layer 406 makes it possible to prevent the ohmic contactlayer from chemically reacting with a drain electrode, which will beformed.

[0045] As shown in FIG. 4B, the semiconductor layer 404, the ohmiccontact layer 405 and the buffer layer 406 of titanium, which are formedon the gate insulating film 403, are patterned. Then, as shown in FIG.4C, the transparent conductive film for the pixel electrode, such asITO, is formed on the buffer layer 406 by a sputtering process, and ispatterned so that a transparent electrode 407 is formed.

[0046] As shown in FIG. 4D, the source and drain electrodes 408 and 409are formed of one of aforementioned low resistance metals to connectwith the transparent electrode 407 for the pixel electrode on the bufferlayer 406.

[0047] As shown in FIG. 4E, the passivation layer 410 is deposited onthe entire surface of the insulating substrate 401 including the sourceand drain electrodes 408 and 409, and then the common electrode 411 isformed on the passivation layer 410.

[0048] Afterwards, a liquid crystal layer is formed between theinsulating substrate 401 and an opposing substrate provided with acolor-filter and a black matrix (not shown), so that the manufacturingprocess steps of the in-plane switching mode LCD device according to thepresent invention are completed.

[0049] As has been explained, the in-plane switching mode LCD device andthe method for manufacturing the same according to the present inventionhave the following advantages.

[0050] In the in-plane switching mode LCD device according to thepresent invention, brightness and aperture ratio can be improved withoutan additional mask. Also, the buffer layer comprising titanium (Ti) isdeposited on the ohmic contact layer, so that the etching selectivitybetween the source and drain electrodes and the transparent conductivefilm is improved, and the buffer layer makes it possible to prevent achemical reaction between the source and drain electrodes and the ohmiccontact layer. Accordingly, the low resistance materials such asaluminum (Al), copper (Cu) and silver (Ag), can be used as the sourceand drain electrodes, so that the in-plane switching mode LCD device isapplicable to the LCD device having fineness and a large size.

[0051] It will be apparent to those skilled in the art that variousmodifications and variation can be made in the present invention withoutdeparting from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A liquid crystal display device comprising: athin film transistor within a pixel region defined by a plurality ofgate lines and data lines; and a buffer layer interposed between a gateelectrode and source and drain electrodes of the thin film transistor,the source and drain electrodes having a low resistance material.
 2. Thedevice as claimed in claim 1, wherein the buffer layer includes a metal.3. The device as claimed in claim 1, wherein the buffer layer includestitanium (Ti).
 4. The device as claimed in claim 1, wherein the gateelectrode includes a low resistance material.
 5. The device as claimedin claim 4, wherein the low resistance material includes one of aluminum(Al), copper (Cu), and silver (Ag).
 6. The device as claimed in claim 1,wherein the low resistance material includes one of aluminum (Al),copper (Cu), and silver (Ag).
 7. An in-plane switching mode liquidcrystal display (LCD) device comprising: a thin film transistor having asource electrode, a drain electrode, and a gate electrode within a pixelregion defined by a plurality of gate lines and data lines, the sourceand drain electrodes having a low resistance material; an ohmic contactlayer on the active region; and a buffer layer on the ohmic contactlayer; wherein the source and drain electrodes are on the buffer layer.8. The in-plane switching mode LCD device as claimed in claim 7, whereinthe gate electrode includes a low resistance material.
 9. The in-planeswitching mode LCD device as claimed in claim 8, wherein the lowresistance material includes one of aluminum (Al), copper (Cu), andsilver (Ag).
 10. The in-plane switching mode LCD device as claimed inclaim 7, wherein the low resistance material includes one of aluminum(Al), copper (Cu) and silver (Ag).
 11. The in-plane switching mode LCDdevice as claimed in claim 7, wherein the buffer layer includes a metal.12. The in-plane switching mode LCD device as claimed in claim 7,wherein the buffer layer includes titanium (Ti).
 13. The in-planeswitching mode LCD device as claimed in claim 7, further comprising agate insulating film on an entire surface including the gate electrode.14. The in-plane switching mode LCD device as claimed in claim 13,wherein the gate insulating film includes one of silicon nitride filmand silicon oxide film.
 15. The in-plane switching mode LCD device asclaimed in claim 7, further comprising a pixel electrode electricallyconnected with the buffer layer.
 16. The in-plane switching mode LCDdevice as claimed in claim 15, wherein the pixel electrode includestransparent conductive material.
 17. The in-plane switching mode LCDdevice as claimed in claim 16, wherein the transparent conductivematerial includes indium tin oxide.
 18. An in-plane switching modeliquid crystal display (LCD) device comprising: a gate electrode on asubstrate; a gate insulating film on an entire surface of the substrate;a semiconductor layer and an ohmic contact layer on the gate insulatingfilm; a buffer layer on the ohmic contact layer; a pixel electrode onthe buffer layer; source and drain electrodes connected with the pixelelectrode on the buffer layer; a passivation layer on the pixelelectrode; and a common electrode on the passivation layer.
 19. Thein-plane switching mode LCD device as claimed in claim 18, wherein thegate electrode includes a low resistance material.
 20. The in-planeswitching mode LCD device as claimed in claim 19, wherein the lowresistance material includes one of aluminum (Al), copper (Cu), andsilver (Ag).
 21. The in-plane switching mode LCD device as claimed inclaim 18, wherein the buffer layer includes a metal.
 22. The in-planeswitching mode LCD device as claimed in claim 21, wherein the bufferlayer includes titanium (Ti).
 23. The in-plane switching mode LCD deviceas claimed in claim 18, wherein the source and drain electrodes includea low resistance material.
 24. The in-plane switching mode LCD device asclaimed in claim 23, wherein the low resistance material includes one ofaluminum (Al), copper (Cu), and silver (Ag).
 25. The in-plane switchingmode LCD device as claimed in claim 18, wherein the pixel electrodeincludes transparent conductive material.
 26. The in-plane switchingmode LCD device as claimed in claim 25, wherein the pixel electrodeincludes indium tin oxide.
 27. The in-plane switching mode LCD device asclaimed in claim 18, wherein the common electrode includes indium tinoxide.
 28. A method for manufacturing an in-plane switching mode liquidcrystal display (LCD) device comprising: forming a gate electrode on asubstrate; forming a gate insulating film, a semiconductor layer, anohmic contact layer, and a buffer layer on the gate electrode; forming apixel electrode on the buffer layer; forming source and drain electrodeson the buffer layer; forming a passivation layer on a surface of thesubstrate; and forming a common electrode on the passivation layer. 29.The method as claimed in claim 28, wherein the gate electrode includesone of aluminum (Al), copper (Cu), and silver (Ag).
 30. The method asclaimed in claim 28, wherein the buffer layer includes titanium (Ti).31. The method as claimed in claim 28, wherein the source and drainelectrodes include one of aluminum (Al), copper (Cu), and silver (Ag).32. The method as claimed in claim 28, wherein the pixel electrodeincludes indium tin oxide.
 33. The method as claimed in claim 28,wherein the drain electrode is electrically connected with the pixelelectrode.
 34. The method as claimed in claim 28, wherein the commonelectrode includes indium tin oxide.
 35. The method as claimed in claim28, wherein the gate electrode is deposited by a sputtering process. 36.The method as claimed in claim 35, wherein the gate electrode ispatterned using photolithography.
 37. The method as claimed in claim 28,wherein the semiconductor layer, the ohmic contact layer, and the bufferlayer are formed on the gate insulating film by a plasma enhancedchemical vapor deposition (PECVD) process.
 38. The method as claimed inclaim 37, wherein the semiconductor layer, the ohmic contact layer, andthe buffer layer are patterned.
 39. The method as claimed in claim 28,wherein the pixel electrode is formed by a sputtering process.
 40. Themethod as claimed in claim 39, wherein the pixel electrode is patterned.41. The method as claimed in claim 28, wherein the passivation layer isformed by a deposition process.